<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>width过渡</title>
    <style>
    div{
    	width: 200px;
    	background: #61E8E1;
    	height: 200px;
    	transition: width 2s;
    }

    div:hover {
    	width: 500px;
    }

    </style>
</head>

<body>
    <p><b>注意：</b>该实例无法在 Internet Explorer 9 及更早 IE 版本上工作。</p>
    <div></div>
    <p>鼠标移动到 div 元素上，查看过渡效果。</p>
</body>

</html>